1. Field of the Invention
The present invention relates to a thin film device having a thin film element functioning electrically or magnetically, and a thin film device module provided with a thin film device, as well as a method of forming a thin film device module.
2. Description of the Related Art
In general, a semiconductor device or a thin film device having a functional film such as a magnetic sensor is secured with adhesive to a conductive substrate such as a lead frame. For example, as shown in FIG. 8, a thin film device 120, which includes a functional film 123 disposed on a surface of a conductive substrate 121 of silicon (Si) or the like with an insulating film 122 in between, is fixed to a lead frame 130 with an adhesive layer 140 in between. Typically, however, the adhesive layer 140 is an insulator and therefore electric charge is apt to accumulate in the functional film 123, so that its surface potential may rise momentarily. Especially, as the thin film device 120 becomes smaller, it is more apt to be adversely affected. In some cases, the potential may rise up to about 10000 V, for example, with a slight amount of application of electric charge to the lead frame 130. In that case, due to a potential difference between the surface of the lead frame 130 and the surface of the functional film 123, electro-static discharge (hereinafter referred to as “ESD”) will occur, causing damage or malfunction in the functional film 123.
As a method of connecting a lead frame and a thin film device, one is to use a conductive adhesive containing conductive filler instead of an insulating adhesive. The suppression of a rapid rise of the potential in the functional film may be expected by so doing. The conductive adhesive is one having an electric resistivity (a specific electric resistance) of about 1 to 10 Ω·cm, which is for example disclosed in Japanese Patent No. 2893782. With this method, it is possible to reduce the potential of the surface of the thin film device (the functional film) to the same level as the surface of the lead frame, and yet stabilize the potential.